The invention relates to robot manipulators in general, and more particularly to improvements in robot arms. Still more particularly, the invention relates to improvements in industrial robot arms which can be utilized in or with portal type overhead conveyors, for example, to transport stacks of tied-together flat cardboard blanks, rolls of convoluted (i.e., wound or rolled) flexible sheet material or the like, e.g., in tobacco processing plants.
Robot arms which form part of or constitute portal type overhead conveyors are or can be used in many branches of the tobacco processing industry. For example, such apparatus (hereinafter called manipulators for short) can be utilized to deliver fresh bobbins of convoluted paper or other flexible sheet material as well as to remove empty bobbins from bobbin changers which are utilized in cigarette makers to supply a continuous web of cigarette paper to a wrapping station where the web is draped around a continuous rod-like filler of natural, reconstituted and/or substitute tobacco. Furthermore, such manipulators can be used in cigarette packing machines to transfer stacks of blanks from pallets to conveyors which deliver the stacks to the packing machine proper. For example, the blanks can be converted into the containers of so-called hinge lid packets for arrays of four, five, ten, twenty or twentyone plain or filter cigarettes.
Published German patent application No. 33 44 903 discloses a gripper for use on the arm of an industrial robot. The robot arm carries a pivotable twin arm the ends of which carry rapid-action couplings for attachment of specially designed grippers serving to manipulate printed circuit boards and foils. A drawback of the robot arm which is disclosed in the aforementioned published German patent application is that it does not include any means for supporting a load from below. Thus, a printed circuit board is lifted, held and transported solely by suction which is unsatisfactory because the robot arm cannot carry out rapid movements such as would be likely to overcome the suction force between the printed circuit board and a suction-operated gripper, i.e., movements which would entail the generation of acceleration forces greater than the suction between a gripper and the load which is suspended thereon solely by suction. Moreover, the robot arm is not capable of directly accepting and transferring loads, i.e., it is necessary to furnish the manipulator with a number of specifically designed grippers, one for each type of load.
Published German patent application No. 35 02 182 discloses a system which is designed to accurately adjust the gripper of a robot which is provided with means for supporting the load from below. The supporting means is pivotable between an idle position and an operative position in response to actuation of a linkage. The gripper is designed to engage the sides of a load; therefore, such gripper cannot be used to lift and transport objects which are stacked on a pallet or the like in close or immediate proximity to each other. Another draback of the just described manipulator is that it must be equipped with a complex, bulky and expensive mechanism for powering its supporting means.
Published German patent application No. 40 28 150 discloses a manipulator which is to be used to supply stacks of sheets to a packing machine. The gripper is designed in such a way that it can manipulate only complete series of stacks, i.e., the versatility of the manipulator is highly unsatisfactory because it is designed to manipulate only a single type of load.
European patent application No. 0 411 523 discloses a manipulator which is designed to transport tied-together stacks of sheet-like objects, such as for example stacks of tied-together flat blanks which are to be converted into containers in packing machines. The manipulator comprises a head with grippers serving to engage stacks of blanks. The specific example which is disclosed in the European patent application employs suction-operated grippers which cooperate with means for supporting the stacks from below. This is to ensure that the grippers can rapidly transfer stacks of superimposed blanks which are to be utilized in the packing machine. A drawback of the just described manipulator is that it must be equipped with a specially designed head for reception of stacked blanks and also that a specially designed actuating mechanism must be provided to operate the supporting means which prop the stacks from below. All this reduces the versatility of the manipulator, i.e., the manipulator which is disclosed in the European patent application is not readily convertible for the manipulation of different loads. Moreover, the conversion is expensive and time consuming.